As displays of mobile electronic devices such as mobile phones, television sets, personal computers, or the like, liquid crystal display devices are widely used. In general, liquid crystal display devices exhibit excellent display performances when a display screen is viewed from a front surface side. Meanwhile, when the display screen is viewed from an oblique direction, contrast is lowered, and thus the visibility is likely to deteriorate. Alternatively, gray scale inversion may occur in which brightness is reversed in gray scale display. Therefore, various techniques of widening a viewing angle range at which a screen is observable with good visibility have been proposed. As one means for improving the viewing angle of the liquid crystal display device, a method using an optical compensating plate such as a retardation plate is known, and various retardation plates have been proposed.
For example, PTL 1 below discloses a liquid crystal display device including a liquid crystal cell of a twisted nematic (hereinafter, abbreviated as TN) mode, a pair of polarizers arranged on both surfaces of the liquid crystal cell, and positive A-type retardation layers respectively arranged between the liquid crystal cell and the polarizers. Further, PTL 2 below discloses a liquid crystal display device including a liquid crystal cell having a liquid crystal layer with negative dielectric anisotropy, a pair of polarizers arranged on both surface of the liquid crystal cell, and a biaxial film as a retardation compensation element provided between at least one of the pair of polarizers and the liquid crystal cell.
As another means for improving the viewing angle of the liquid crystal display device, a configuration has been proposed in which a member for scattering light emitted from a liquid crystal panel is provided on a viewing side of the liquid crystal panel. For example, PTL 3 below discloses a transmission display device including a light diffusion sheet having a light diffusion layer in which a plurality of grooves having approximately V-shaped cross section are formed in parallel in a one-dimensional direction or two-dimensional directions, on a viewing side of the liquid crystal panel.
PTL 4 discloses a liquid crystal display device including a liquid crystal cell and an optical compensation polarizer. The optical compensation polarizer is arranged on at least one of a light incident side or a light emission side of the liquid crystal cell. The optical compensation polarizer includes a polarizer, a birefringent layer, and an anisotropic scattering film.
PTL 5 discloses a liquid crystal display device including a liquid crystal display panel and a light diffusion sheet. The light diffusion sheet is arranged on a light emission side of the liquid crystal display panel.
The light diffusion sheet has a low refractive index region and a high refractive index region. The cross-sectional shape of the low refractive index region is approximated to an isosceles triangle. The high refractive index region is arranged around the low refractive index region.